1. Field of the Invention
The present invention relates generally to a hand tool, and more particularly to a torque wrench.
2. Description of the Related Art
FIG. 1 shows a conventional mechanical torque wrench 10. The shank body 12 of the torque wrench 10 is formed with a window 13. A scale plate 14 is disposed in the shank body 12. The scales 15 of the scale plate 14 can be seen through the window 13. A handle 16 is rotatably disposed at a rear end of the shank body 12. Scales 17 are disposed on a circumference of the handle 16. The torque value of the wrench is adjustable by means of rotating the handle 16. When rotating the handle 16, the scale plate 14 is indirectly driven by the handle 16 to move. A user can read the scales 15, 17 to find the set torque value of the wrench. The torque value is read in a manner similar to that of a caliper.
FIG. 2 shows another conventional mechanical torque wrench 20. The shank body 22 of the torque wrench 20 is marked with scales 25. The torque value of the wrench 20 is adjustable by means of rotating the handle 26. When rotating the handle 26, the handle 26 is also axially moved along the shank body 22. A user can read the scales 27 marked on the handle 26 and the scales 25 aligned with the front end of the handle 26 to find the set torque value of the wrench.
Both the above conventional torque wrenches cannot be quickly adjusted in torque value. Also, it is inconvenient to adjust the torque value of the conventional torque wrenches. For example, the torque value can be increased or decreased by 10 Nm by means of rotating the handle 16 or 26 by one circle. Therefore, it is necessary to rotate the handle by six circles for adjusting the torque value of the wrench by 60 Nm. There are several often used torque values in many sites such as an automobile service shop where several torque values are often used for the tire of an automobile. The torque values are frequently switched in the automobile service shop. The conventional torque wrenches cannot be quickly adjusted in torque value so that it is inconvenient to use the conventional torque wrenches.
In addition, the scales 15, 25 of the conventional torque wrenches are too small to clear see. Moreover, the conventional torque wrenches are marked with different units of scales such as Nm of international unit, lb-ft of British system and kg-m of metric system. These scales of different units are densely arranged so that it is hard for a user to clearly identify the torque values. In conversion between different units, the user often guesses or adjusts the torque value of the wrench to an approximate range without precisely setting a true torque value.
According to the above, the conventional torque wrench has the shortcomings that the torque cannot be quickly adjusted and it is hard to read the torque value.